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Practices which infiltrate surface runoff through an engineered soil or filter media, and discharge through an underdrain include [[stormwater planters]] and some forms of [[bioretention]].
Practices which infiltrate surface runoff through an engineered soil or filter media, and discharge through an underdrain include [[stormwater planters]] and some forms of [[bioretention]].
The maximum flow rate from the BMP may be limited by the hydraulic conductivity of the mmedium, or by the properties of the perforated [[pipe]].
The maximum flow rate from the BMP may be limited by the hydraulic conductivity of the medium, or by the properties of the perforated [[pipe]].
The maximum flow rate through a bed of filer media (''Q<sub>max</sub>'', L/s) may be calculated:
The maximum flow rate through a bed of filter media (''Q<sub>max, m</sub>'', L/s) may be calculated:
<math>Q_{max}=\frac{K_{m}\times A_{p}\times \left (\frac{\sum d}{d_{m}} \right )}{3600}</math>
<math>Q_{max, m}=\frac{K_{m}\times A_{p}\times \left (\frac{\sum d}{d_{m}} \right )}{3600}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''K<sub>m</sub>'' is the hydraulic conductivity of the filter media (mm/hr),
*''K<sub>m</sub>'' is the hydraulic conductivity of the filter media (mm/hr),
===Example calculation===
===Example calculation===
A [[stormwater planter]] with footprint of 8 x 1.5 m is planned to received runoff from an adjacent rooftop. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. The underdrain pipe will be embedded into high performance bedding or similar, with a strip of geotextile over the top to prevent migration of the filter media into the pipe. The lab test states that the medium has a hydraulic conductivity of 25 mm/hr. The maximum flow through the medium will be calculated and a comparison made with the maximum flow through the pipe to see....:
A [[stormwater planter]] with footprint of 8 x 1.5 m is planned to received runoff from an adjacent rooftop. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. The underdrain pipe will be embedded into high performance bedding or similar, with a strip of geotextile over the top to prevent migration of the filter media into the pipe. The lab test states that the medium has a hydraulic conductivity of 25 mm/hr. The maximum flow through the medium will be calculated and a comparison made with the maximum flow through the pipe to see....:
<math>Q_{max}=\frac{25 mm/hr\times 12\ m^{2}\times \left (\frac{1.1\ m}{0.75\ m} \right )}{3600\ s/hr}=0.12\ L/s</math>
<math>Q_{max, m}=\frac{25 mm/hr\times 12\ m^{2}\times \left (\frac{1.1\ m}{0.75\ m} \right )}{3600\ s/hr}=0.12\ L/s</math>